1. Field of the Invention
This invention generally relates to channel letter lighting systems, and more particularly to LED based low profile channel letter lighting systems.
2. Description of the Related Art
Display units, such as light boxes, cabinet signs and channel letters are commonly found on the outside of buildings or businesses and are often used to advertise the name of the business or products. Typical light boxes and cabinet signs are constructed of aluminum or plastic housing having the shape of a box and are approximately 5″ deep. The housing sometimes has a swing open frame to allow for easily changing the advertising graphics within. The top opening in the housing, or surface, is covered by a translucent or clear lens that transmits light from within the housing. The advertisement graphic is placed under this lens so that it is between the lens and the lighting units inside the light box. This allows the graphic to be illuminated from behind by the lighting units within the light box. In some cases the translucent lens itself may be the illuminated graphic.
Typical channel letters display units can be constructed of aluminum or plastic housings having the shape of a letter, wherein each housing is an individual structure having separate illumination. Channel letter display units can be produced in almost any font, color or size. Typical channel letter display units are approximately 5 inches deep. The housing has a face, a rear wall, and sidewalls, with a light source within the housing such that the housing emits light out the face and/or the back of the housing.
To enhance the visibility of these display units, different types of lighting units are incorporated. Various types of lighting systems are used with different light sources such as incandescent bulbs, neon bulbs or fluorescent tubes. One of the problems associated with the conventional lighting units and systems is that their light sources can experience relatively short lifespans and they can have relatively low electrical efficiency. Incandescent bulbs, neon bulbs and fluorescent tubes have a relatively short lifespan, particularly when compared to other light sources, such as typical LEDs. These light sources are also electrically inefficient and providing sufficient lighting, especially in large lighting applications, requires the consumption of significant energy. For example, a standard fluorescent tube 60 inches in length consumes as much as 60 to 70 Watts, and conventional display units can utilize many of these tubes. Neon bulbs can also experience difficulty with cold starting, which can lead to failure of the neon bulb.
More recently, with the advent of the efficient solid state lighting sources, these display units have been used with LEDs, for example. LEDs are solid state devices that convert electric energy to light and generally comprise one or more active regions of semiconductor material interposed between oppositely doped semiconductor layers. When a bias is applied across the doped layers, holes and electrons are injected into the active region where they recombine to generate light. Light is produced in the active region and emitted from surfaces of the LED.
LEDs have certain characteristics that make them desirable for many lighting applications that were previously the realm of incandescent, fluorescent or neon lights. Incandescent lights are very energy-inefficient light sources with a vast majority of the electricity they consume being released as heat rather than light. Fluorescent light bulbs are more energy efficient than incandescent light bulbs, but are still relatively inefficient. Neon light tubes need to be bent or formed into the shape corresponding to the housing, which can be labor intensive, especially for channel letter housings. As such, neon tubes are fragile and are more susceptible to breakage during transit and installation. Neon light tubes are powered by 4,000-15,000 Volts AC and present a significantly higher electrical hazard potential. LEDs by contrast, can emit the same luminous flux as incandescent, fluorescent or neon lights using a fraction of the energy.
In addition, LEDs can have a significantly longer operational lifetime. Incandescent light bulbs have relatively short lifetimes, with some having a lifetime in the range of about 750-1,000 hours. Fluorescent bulbs can also have lifetimes longer than incandescent bulbs such as in the range of approximately 10,000-20,000 hours, but provide less desirable color reproduction. In comparison, LEDs can have lifetimes between 50,000 and 70,000 hours.
The increased efficiency and extended lifetime of LEDs is attractive to many lighting suppliers and has resulted in LED lights being used in place of conventional lighting in different sign applications. For example, to illuminate a typical channel letter display unit, an array of LED light units can be mounted to the rear wall and direct light towards the face. To optimize efficiency, the LED light units of the array are typically spaced from one another as far as possible before any dark spots are noticeable on the face. To prevent dark spots, the LED light units are spaced close enough to one another so that the light beam pattern generated by each LED light unit overlaps an adjacent LED light unit as the emitted light contacts the face. The face is thereby illuminated in a generally even manner having no bright spots or dark spots.
Channel letters are also manufactured having a shallow housing depth of approximately 2 inches, which can also be called low profile channel letters. However, mounting the LED light units on the rear wall could result in the channel letter exhibiting bright and/or dark spots on the face because of reduced overlap of emitted light from the LED light units.